Ten-year-old Reen Penterson is spending her summer writing a novel so she can become rich and famous and won't have to go to school anymore. But when she hears a rumor of a treasure hunt in the university town she lives in, she jettisons the novel and enlists the aid of her nine-year-old cousin Joanie to help her find the loot. The adventure begins with a cryptic clue written by the mysterious "Mr. Shadow."

Competing with other teams of young treasure seekers, Reen and Joanie form the R&J Detective Agency and doggedly track clues through the library and around the campus of Bellevue University. But when they decipher a final clue, their solution is stolen by a competitor. All appears lost, but things are never what they seem in Mr. Shadow's world. With just minutes to spare, Reen and Joanie get one last chance to locate the treasure. But can they do it before time runs out?